This invention relates to an integrated optical element used for an optical pickup for recording and/or reproduction of signals by irradiating with a light beam a signal recording surface of an optical type disc (hereinafter referred to as optical disc) such as a mini disc (MD), a magneto-optical disc (MO), a compact disc (CD) or a CD-ROM, an optical pickup using this integrated optical element, and an optical disc device having this optical pickup.
Conventionally, an optical pickup constituted, for example, as shown in FIG. 1 is proposed as an optical pickup for an optical disc. The optical pickup 1 shown in FIG. 1 has a semiconductor laser element 2 as a light source, an optical member 3 made of a transparent material such as glass or plastics, an objective lens 4 for converging a light, and a photodetector 5 for receiving a light and converting the light to an electric signal.
Of these elements constituting the optical pickup 1, the light-emitting element 2, the optical member 3 and the photodetector 5 are integrated as an integrated element, which is provided in the state of being fixed to a base, not shown. The objective lens 4 is provided on the base via a biaxial actuator, not shown. As the biaxial actuator is driven, the objective lens 4 is minutely moved in biaxial directions, that is, in the direction of radius of an optical disc D and in the direction toward and away from the optical disc D.
In this optical pickup, as the base is fed in the direction of radius of the optical disc D by the driving of a thread feed motor, not shown, a desired recording track on the optical disc can be accessed.
In this optical pickup 1, the optical member 3 has two surfaces in parallel to each other. These two surfaces are arranged to be substantially perpendicular to the optical axis of the light beam from the semiconductor laser element 2. On a first surface (lower-center side in FIG. 1) of the optical member 3 on the side of the semiconductor laser element 2, a grating 3a for diffracting a light beam directed toward the optical disc D into the direction corresponding to the direction along the recording track on the optical disc D and for splitting the light beam into a plurality of beams including at least a main beam and two side beams is formed on the optical axis of the light beam from the semiconductor laser element 2.
Also, on a second surface (upper-center surface in FIG. 1) of the optical member 3 on the side of the optical disc D, a hologram 3b for diffracting a return light beam reflected from the signal recording surface of the optical disc D and for guiding the return light beam to the photodetector 5 is formed on the optical axis of the light beam from the semiconductor laser element 2.
The hologram 3b functions as optical path branching means for branching the optical path of the return light beam directed toward the photodetector 5 from the optical path of the light beam directed toward the optical disc D, by diffracting the return light beam from the optical disc D incident on the second surface of the optical member 3 and thus directing the return light beam toward the photodetector 5.
The hologram 3b has two hologram areas 3b-1 and 3b-2 for diffracting the incident return light beam by different diffraction angles, respectively, as shown in FIG. 1. The boundary between these hologram areas 3b-1 and 3b-2 is formed on the second surface of the optical member 3 so as to be substantially coincident with the direction corresponding to the direction of radius of the optical disc D. The return light beam from the optical disc D becomes incident on the hologram 3b with its center located on the boundary between the two hologram areas 3b-1 and 3b-2, and is bisected along the boundary. The bisected portions are diffracted by different diffraction angles, respectively.
That is, the hologram 3b also functions as return light beam splitting means for bisecting the incident return light beam along a splitting line in the direction corresponding to the direction of radius of the optical disc D.
The photodetector 5 has a center light-receiving section 5a for receiving a return light of the main beam, from among the plurality of beams generated by the grating 3a, and light-receiving sections e and f for receiving return lights of the side beams, provided on both sides of the center light-receiving section 5a, specifically, on both sides of the direction corresponding to the direction along the recording track on the optical disc D, as shown in FIG. 1. The center light-receiving section 5a further has four light-receiving sections a, b, c and d which are divided by a division line d1 in the direction corresponding to the direction of radius of the optical disc D and a division line d2 in the direction along the recording track on the optical disc D.
The division line d1 on the center light-receiving section 5a extends in the direction corresponding to the direction of radius of the optical disc D along the direction of diffraction of the hologram 3b in order to prevent generation of any deviation of the focusing error signal level of a light spot in a focused state due to a change in the oscillation wavelength of the semiconductor laser element 2 or due to a change in the refractive index of the optical member 3 by a temperature change.
In this optical pickup 1, the light beam emitted from the semiconductor laser element 2 becomes incident on the optical member 3 from its first surface, then is split into a plurality of beams by the grating 3a, and then passes through the optical member 3. The optical beam which has passed through the optical member 3 is converged by the objective lens 4 and is cast as a fine light spot onto the signal recording surface of the optical disc D. In this case, three light spots are formed on the signal recording surface of the optical disc D by the main beam and two side beams generated by the grating 3a. In FIG. 1, only the main beam is shown.
The light beams cast on the signal recording surface of the optical disc D reflected by the signal recording surface of the optical disc D so as to be return light beams. The return light beams pass again through the objective lens 4 and become incident on the optical member 3 from its second surface. The return light beams incident on the optical member 3 are diffracted by the hologram 3b formed on the second surface of the optical member 3. Specifically, the return light beams become incident on the hologram 3b with their centers located on the boundary between the two hologram areas 3b-1 and 3b-2, and the portions incident on the individual hologram areas 3b-1 and 3b-2 are diffracted by different diffraction angles, respectively. The return light beams diffracted by the hologram areas 3b-1 and 3b-2 of the hologram 3b pass through the optical member 3 so as to be directed toward the photodetector.
Of the return light beams directed toward the photodetector 5, the return light beam which is a return light of the main beam and is diffracted by the one hologram area 3b-1 of the hologram 3b becomes incident on the two light receiving sections a and b of the center light-receiving section 5a of the photodetector 5. Of the return light beams directed toward the photodetector 5, the return light beam which is a return light of the main beam and is diffracted by the other hologram area 3b-2 of the hologram 3b becomes incident on the remaining two light receiving sections c and d of the center light-receiving section 5a of the photodetector 5. Of the return light beams directed toward the photodetector 5, the return light beams of the side beams become incident on the light-receiving sections e and f of the photodetector 5.
The photodetector 5 converts the lights incident on the light-receiving sections a, b, c, d, e and f to electric signals, and supplies the resultant signals to a signal processing circuit, not shown. The detection signals from the photodetector 5 are amplified by head amplifiers in the signal processing circuit so as to be output signals Sa, Sb, Sc, Sd, Se and Sf, and predetermined arithmetic processing is performed thereon by an arithmetic circuit. Thus, a reproduction signal RF0 is generated. Also, a focusing error signal FE0 is generated by a so-called Foucault method and a tracking error signal TR0 is generated by a three-beam method.
The reproduction signal RF0 is calculated, for example, by the arithmetic circuit carrying out arithmetic processing with the following equation (1).
RF0=(Sa+Sb)+(Sc+Sd)xe2x80x83xe2x80x83(1)
The focusing error signal FE0 is calculated, for example, by the arithmetic circuit carrying out arithmetic processing with the following equation (2), (3) or (4).
FE0=Saxe2x88x92Sbxe2x80x83xe2x80x83(2)
FE0=Scxe2x88x92Sdxe2x80x83xe2x80x83(3)
FE0=(Sa+Sd)xe2x88x92(Sc+Sb)xe2x80x83xe2x80x83(4)
The tracking error signal TR0 is calculated, for example, by the arithmetic circuit carrying out arithmetic processing with the following equation (5).
TR0=Sexe2x88x92Sfxe2x80x83xe2x80x83(5)
On the basis of the focusing error signal FE0 thus generated, the optical pickup 1 carries out focusing servo for driving the biaxial actuator to minutely move the objective lens 4 in the direction toward and away from the optical disc D and thus controls the focal point of the light beam converged by the objective lens 4 so as to be constantly located on the signal recording surface of the optical disc D.
In addition, on the basis of the tracking error signal TR0 generated in the above-described manner, the optical pickup 1 carries out tracking servo for driving the biaxial actuator to minutely move the objective lens 4 in the direction of radius of the optical disc D and thus causes the spot of the light beam converged by the objective lens 4 to follow the recording track on the optical disc D.
By thus carrying out focusing servo and tracking servo while recording/reproducing signals to/from the optical disc D, the optical pickup 1 can carry out appropriate signal recording/reproduction even in the case where the optical disc D is fluctuated or tilted.
Meanwhile, in the case where signal recording/reproduction is to be carried out with the optical disc D in the optical pickup 1, the base must be first fed in the direction of radius of the optical disc to access a predetermined recording track, as described above, in the state where tracking servo is off.
The objective lens 4 is provided movably on the base via the biaxial actuator as described above. Therefore, when the base is fed in the direction of radius of the optical disc D or when the feed operation is stopped, the position of the objective lens with respect to the base is deviated in the direction of radius of the optical disc D (to the inner side or outer side of the optical disc D) from the normal position because of inertia, as shown in FIG. 2.
The deviation of the objective lens 4 from the normal position is eliminated with the lapse of a predetermined time period. However, during this time period for recovering the position of the objective lens 4, recording/reproduction of signals to/from the optical disc cannot be carried out. This is one element that substantially disturbs the high-speed access property of the optical pickup 1.
To realize the high-speed property of such optical pickup 1, the position of the objective lens 4 may be instantaneously recovered by detecting the deviation of the objective lens 4 from the normal position, then feeding the detected deviation back to the biaxial actuator, and controlling the driving of the biaxial actuator to eliminate the deviation of the objective lens 4.
To detect the deviation of the objective lens 4 from the normal position, there is considered, for example, a technique of attaching a position sensor to the objective lens 4 so as to detect the actual position of the objective lens 4 by the position sensor and thus detecting the position deviation of the objective lens 4 from the actual position of the objective lens 4 and the quantity of feeding of the base.
However, this technique requires the position sensor for detecting the position of the objective lens 4 to be separately provided in the optical pickup 1, and therefore causes problems such as the increase in the number of components, increase in size of the optical pickup 1 and rise in cost.
In view of the foregoing status of the art, it is an object of the present invention to provide an optical pickup which realizes the high-speed access property by appropriately and simply detecting the position deviation of the objective lens as the light beam converging means at the time of access without adding any new component, an integrated optical element used therefor, and an optical disc device having this optical pickup.
An integrated optical element according to the present invention, used for an optical pickup for carrying out recording and/or reproduction of signals by irradiating a signal recording surface of an optical disc with a light beam, includes: a light source for emitting the light beam; a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc; a package member for housing the light source and the photodetector therein; an optical member arranged on the package member for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector; and optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam directed toward the photodetector.
In this integrated optical element, the optical path branching means has at least two diffraction areas for diffracting the return light beam reflected by the signal recording surface of the optical disc, into different directions, respectively, and the boundary between the diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving a return light beam diffracted by one diffraction area of the optical path branching means and a portion for receiving a return light beam diffracted by the other diffraction area.
In the integrated optical element according to the present invention, the light source is housed inside the package member and emits the light beam for irradiating the signal recording surface of the optical disc. The light beam emitted from the light source is transmitted through the optical member provided on the package member. Then, the light beam transmitted through the optical member is converged by light beam converging means of the optical pickup and then cast onto the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
Since the optical path branching means has at least two diffraction areas for diffracting the return light beam in different directions, the return light beams incident on the respective diffraction areas of the optical path branching means are diffracted into different directions by the diffraction areas of the optical path branching means, then transmitted through the optical member, and directed toward the photodetector housed in the package member.
Since at least one light receiving section of the photodetector is divided into the portion for receiving the return light beam diffracted by one diffraction area of the optical path branching means and the portion for receiving the return light beam diffracted by the other diffraction area, the return light beams diffracted into different directions by the respective diffraction areas of the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector.
Thus, on the basis of the detection signal from the light-receiving section of the photodetector, a reproduction signal is generated and a focusing error signal is generated by a so-called Foucault method.
Meanwhile, in the case where the position of the light beam converging means with respect to the integrated optical element is deviated in the direction of radius of the optical disc from the normal position at the time of access to a desired recording track on the optical disc, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In the integrated optical element according to the present invention, the optical path branching means has at least two diffraction areas for diffracting the return light beam into different directions, and the boundary between these diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the optical path branching means. The individual parts of the return light beam generated by asymmetrical splitting by the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the integrated optical element can be detected on the basis of the detection signal from the light-receiving section of the photodetector.
According to the integrated optical element of the present invention, since the position deviation of the light beam converging means with respect to the integrated optical element at the time of access to a desired recording track on the optical disc can be detected in the above-described manner, the optical pickup using this integrated optical element can realize the high-speed access property.
Also, in this integrated optical element, the optical path branching means for separating the optical path of the return light beam directed toward the photodetector from the optical path of the light beam emitted from the light source and for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the integrated optical element, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical pickup using this integrated optical element can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
In the integrated optical element according to the present invention, it is desired that light beam splitting means for diffracting the light beam directed toward the optical disc and for splitting the light beam into a plurality of beams including a main beam and two side beams is formed integrally with the optical member.
As the light beam splitting means for diffracting and splitting the light beam directed toward the optical disc into a plurality of beams is provided, as described above, the integrated optical element according to the present invention forms spots of the main beam and two side beams onto the signal recording surface of the optical disc and detects the return light beams thereof. Thus, a tracking error signal can be generated by a so-called three-beam method.
Moreover, as the light beam splitting means is formed integrally with the optical member, as described above, the integrated optical element according to the present invention can realize miniaturization of the integrated optical element itself and miniaturization of the optical pickup using this integrated optical element.
Also, in the integrated optical element according to the present invention, it is desired that at least one light-receiving section of the photodetector is divided by division lines substantially parallel to the boundary of the diffraction areas of the optical path branching means.
As at least one light-receiving section of the photodetector is divided by the division lines substantially parallel to the boundary of the diffraction areas of the optical path branching means, as described above, the integrated optical element according to the present invention can effectively restrain generation of any deviation of the signal level of the focusing error signal due to a position change of the return light spot and detect an appropriate focusing error signal even in the case where the position of the return light spot of the light beam in a focused state on the photodetector is somewhat changed by a change in the oscillation wavelength of the light source or by a change in the refractive index of the optical member due to a temperature change.
Another integrated optical element according to the present invention, used for an optical pickup for carrying out recording and/or reproduction of signals by irradiating a signal recording surface of an optical disc with a light beam, includes: a light source for emitting the light beam; a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc; a package member for housing the light source and the photodetector therein; an optical member arranged on the package member for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector; optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam reflected by the signal recording surface of the optical disc; and return light beam splitting means integrally formed with the optical member for splitting the return light beam passed through the optical path branching means into at least two beams.
In this integrated optical element, the return light beam splitting means has at least two surfaces having different normal vectors, and the boundary between these surfaces is inclined at a predetermined angle with respect to a direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving one return light beam generated by the return light beam splitting means and a portion for receiving the other return light beam.
In this another integrated optical element according to the present invention, the light source is housed inside the package member and emits the light beam for irradiating the signal recording surface of the optical disc. The light beam emitted from the light source is transmitted through the optical member provided on the package member. Then, the light beam transmitted through the optical member is converged by light beam converging means of the optical pickup and then cast onto the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
The return light beam having its optical path branched by the optical path branching means is then split into at least two beams by the return light beam splitting means integrally formed with the optical member.
Since the return light beam splitting means has at least two surfaces having different normal vectors, the return light beam incident on the return light beam splitting means is split along the boundary between the surfaces. The beams generated by splitting proceed in different directions in accordance with the normal vectors of the surfaces on which they are incident, and are directed toward the photodetector housed in the package member.
Since at least one light receiving section of the photodetector is divided into the portion for receiving one return light beam generated by the return light beam splitting means and the portion for receiving the other return light beam, the return light beams generated by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector.
Thus, on the basis of the detection signal from the light-receiving section of the photodetector, a reproduction signal is generated and a focusing error signal is generated by a so-called Foucault method.
Meanwhile, in the case where the position of the light beam converging means with respect to the integrated optical element is deviated in the direction of radius of the optical disc from the normal position at the time of access to a desired recording track on the optical disc, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In this another integrated optical element according to the present invention, the return light beam splitting means has at least two surfaces of different normal vectors and the boundary between these surfaces is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the return light beam splitting means. The individual parts of the return light beam generated by asymmetrical splitting by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the integrated optical element can be detected on the basis of the detection signal from the light-receiving section of the photodetector.
According to this another integrated optical element of the present invention, since the position deviation of the light beam converging means with respect to the integrated optical element at the time of access to a desired recording track on the optical disc can be detected in the above-described manner, the optical pickup using this integrated optical element can realize the high-speed access property.
Also, in this another integrated optical element, the return light beam splitting means for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the integrated optical element, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical pickup using this integrated optical element can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
In this another integrated optical element according to the present invention, it is desired that light beam splitting means for diffracting the light beam directed toward the optical disc and for splitting the light beam into a plurality of beams including a main beam and two side beams is formed integrally with the optical member.
As the light beam splitting means for diffracting and splitting the light beam directed toward the optical disc into a plurality of beams is provided, as described above, this another integrated optical element according to the present invention forms spots of the main beam and two side beams onto the signal recording surface of the optical disc and detects the return light beams thereof. Thus, a tracking error signal can be generated by a so-called three-beam method.
Moreover, as the light beam splitting means is formed integrally with the optical member, as described above, this another integrated optical element according to the present invention can realize miniaturization of the integrated optical element itself and miniaturization of the optical pickup using this integrated optical element.
Also, in this another integrated optical element according to the present invention, it is desired that at least one light-receiving section of the photodetector is divided by division lines substantially parallel to the boundary of the return light beam splitting means.
As at least one light-receiving section of the photodetector is divided by the division lines substantially parallel to the boundary of the diffraction areas of the optical path branching means, as described above, the integrated optical element according to the present invention can effectively restrain generation of any deviation of the signal level of the focusing error signal due to a position change of the return light spot and detect an appropriate focusing error signal even in the case where the position of the return light spot of the light beam in a focused state on the photodetector is somewhat changed by a change in the oscillation wavelength of the light source or by a change in the refractive index of the optical member due to a temperature change.
An optical pickup according to the present invention for carrying out recording and/or reproduction of signals by irradiating a signal recording surface of an optical disc with a light beam includes: a light source for emitting the light beam; light beam converging means for converging the light beam emitted from the light source and for irradiating the signal recording surface of the optical disc with the converged light beam; a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc; an optical member arranged between the light source and photodetector on one side and the light beam converging means on the other side, for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector; optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam directed toward the photodetector; and a biaxial actuator for moving the light beam converging means into biaxial directions, that is, the direction of radius of the optical disc and the direction toward and away from the optical disc.
In this optical pickup, the optical path branching means has at least two diffraction areas for diffracting the return light beam reflected by the signal recording surface of the optical disc, into different directions, respectively, and the boundary between the diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving a return light beam diffracted by one diffraction area of the optical path branching means and a portion for receiving a return light beam diffracted by the other diffraction area.
In the optical pickup according to the present invention, the light beam emitted from the light source is transmitted through the optical member and directed toward the light beam converging means. The light beam is then converged by light beam converging means and then cast onto the signal recording surface of the optical disc.
In the case where the spot of the light beam cast on the signal recording surface of the optical disc is deviated from a predetermined recording track on the signal recording surface of the optical disc, or in the case where no focal point is formed on the signal recording surface of the optical disc, the biaxial actuator is driven on the basis of a tracking error signal or a focusing error signal, and the light beam converging means is moved by the biaxial actuator into the direction of radius of the optical disc or into the direction toward and away from the optical disc. Thus, the spot of the light beam converged by the light beam converging means and cast onto the signal recording surface of the optical disc constantly follows a predetermined recording track on the signal recording surface of the optical disc and forms a focal point on the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
Since the optical path branching means has at least two diffraction areas for diffracting the return light beam in different directions, the return light beams incident on the respective diffraction areas of the optical path branching means are diffracted into different directions by the diffraction areas of the optical path branching means, then transmitted through the optical member, and directed toward the photodetector.
Since at least one light receiving section of the photodetector is divided into the portion for receiving the return light beam diffracted by one diffraction area of the optical path branching means and the portion for receiving the return light beam diffracted by the other diffraction area, the return light beams diffracted into different directions by the respective diffraction areas of the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector.
Thus, on the basis of the detection signal from the light-receiving section of the photodetector, a reproduction signal is generated and a focusing error signal is generated by a so-called Foucault method.
Meanwhile, in the case where the position of the light beam converging means with respect to the optical member is deviated in the direction of radius of the optical disc from the normal position at the time of access to a desired recording track on the optical disc, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In the optical pickup according to the present invention, the optical path branching means has at least two diffraction areas for diffracting the return light beam into different directions, and the boundary between these diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the optical path branching means. The individual parts of the return light beam generated by asymmetrical splitting by the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the optical member can be detected on the basis of the detection signal from the light-receiving section of the photodetector.
According to the optical pickup of the present invention, since the position deviation of the light beam converging means with respect to the optical member at the time of access to a desired recording track on the optical disc can be detected in the above-described manner, the position of the light beam converging means can be instantaneously recovered to secure the accuracy and stability of the access operation and to realize the high-speed access property.
Also, in this optical pickup according to the present invention, the optical path branching means for separating the optical path of the return light beam directed toward the photodetector from the optical path of the light beam emitted from the light source and for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the optical member, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical pickup can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
Another optical pickup according to the present invention for carrying out recording and/or reproduction of signals by irradiating a signal recording surface of an optical disc with a light beam includes: a light source for emitting the light beam; light beam converging means for converging the light beam emitted from the light source and for irradiating the signal recording surface of the optical disc with the converged light beam; a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc; an optical member arranged between the light source and photodetector on one side and the light beam converging means on the other side, for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector; optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam reflected by the signal recording surface of the optical disc; return light beam splitting means integrally formed with the optical member for splitting the return light beam passed through the optical path branching means into at least two beams; and a biaxial actuator for moving the light beam converging means into biaxial directions, that is, the direction of radius of the optical disc and the direction toward and away from the optical disc.
In this optical pickup, the return light beam splitting means has at least two surfaces having different normal vectors, and the boundary between these surfaces is inclined at a predetermined angle with respect to a direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving one return light beam generated by the return light beam splitting means and a portion for receiving the other return light beam.
In this another optical member according to the present invention, the light beam emitted from the light source is transmitted through the optical member and directed toward the light beam converging means. Then, the light beam is converged by light beam converging means and then cast onto the signal recording surface of the optical disc.
In the case where the spot of the light beam cast on the signal recording surface of the optical disc is deviated from a predetermined recording track on the signal recording surface of the optical disc, or in the case where no focal point is formed on the signal recording surface of the optical disc, the biaxial actuator is driven on the basis of a tracking error signal or a focusing error signal, and the light beam converging means is moved by the biaxial actuator into the direction of radius of the optical disc or into the direction toward and away from the optical disc. Thus, the spot of the light beam converged by the light beam converging means and cast onto the signal recording surface of the optical disc constantly follows a predetermined recording track on the signal recording surface of the optical disc and forms a focal point on the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
The return light beam having its optical path branched by the optical path branching means is then split into at least two beams by the return light beam splitting means integrally formed with the optical member.
Since the return light beam splitting means has at least two surfaces having different normal vectors, the return light beam incident on the return light beam splitting means is split along the boundary between the surfaces. The beams generated by splitting proceed in different directions in accordance with the normal vectors of the surfaces on which they are incident, and are directed toward the photodetector.
Since at least one light receiving section of the photodetector is divided into the portion for receiving one return light beam generated by the return light beam splitting means and the portion for receiving the other return light beam, the return light beams generated by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector.
Thus, on the basis of the detection signal from the light-receiving section of the photodetector, a reproduction signal is generated and a focusing error signal is generated by a so-called Foucault method.
Meanwhile, in the case where the position of the light beam converging means with respect to the optical member is deviated in the direction of radius of the optical disc from the normal position at the time of access to a desired recording track on the optical disc, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In this another optical pickup according to the present invention, the return light beam splitting means has at least two surfaces of different normal vectors and the boundary between these surfaces is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the return light beam splitting means. The individual parts of the return light beam generated by asymmetrical splitting by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the optical member can be detected on the basis of the detection signal from the light-receiving section of the photodetector.
According to this another optical pickup of the present invention, since the position deviation of the light beam converging means with respect to the optical member at the time of access to a desired recording track on the optical disc can be detected in the above-described manner, the position of the light beam converging means can be instantaneously recovered to secure the accuracy and stability of the access operation and to realize the high-speed access property.
Also, in this another optical pickup according to the present invention, the return light beam splitting means for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the optical member, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical pickup can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
An optical disc device according to the present invention includes: disc rotating means for rotating an optical disc; an optical pickup for carrying out recording and/or reproduction of signals by irradiating with a light beam a signal recording surface of the optical disc rotated by the disc rotating means; a signal processing circuit for processing a detection signal from the optical pickup; and an access mechanism for moving the optical pickup in the direction of radius of the optical disc.
In this optical disc device, the optical pickup includes a light source for emitting the light beam, light beam converging means for converging the light beam emitted from the light source and for irradiating the signal recording surface of the optical disc with the converged light beam, a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc, an optical member arranged between the light source and photodetector on one side and the light beam converging means on the other side, for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector, optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam directed toward the photodetector, and a biaxial actuator for moving the light beam converging means into biaxial directions, that is, the direction of radius of the optical disc and the direction toward and away from the optical disc. The optical path branching means has at least two diffraction areas for diffracting the return light beam reflected by the signal recording surface of the optical disc, into different directions, respectively, and the boundary between the diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving a return light beam diffracted by one diffraction area of the optical path branching means and a portion for receiving a return light beam diffracted by the other diffraction area.
In the optical disc device according to the present invention, the optical disc as a recording medium is rotated by the disc rotating means. Then, when signals are to be recorded to and/or reproduced from the optical disc rotated by the disc rotating means, a light beam is first emitted from the light source of the optical pickup to the optical disc rotated by the disc rotating means. The optical pickup is moved in the direction of radius of the optical disc by the access mechanism so as to access a desired recording track.
The light beam emitted from the light source is transmitted through the optical member and directed toward the light beam converging means. The light beam is then converged by light beam converging means and then cast onto the signal recording surface of the optical disc.
In the case where the spot of the light beam cast on the signal recording surface of the optical disc is deviated from a predetermined recording track on the signal recording surface of the optical disc, or in the case where no focal point is formed on the signal recording surface of the optical disc, the biaxial actuator is driven on the basis of a tracking error signal or a focusing error signal from the signal processing circuit, and the light beam converging means is moved by the biaxial actuator into the direction of radius of the optical disc or into the direction toward and away from the optical disc. Thus, the spot of the light beam converged by the light beam converging means and cast onto the signal recording surface of the optical disc constantly follows a predetermined recording track on the signal recording surface of the optical disc and forms a focal point on the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
Since the optical path branching means has at least two diffraction areas for diffracting the return light beam in different directions, the return light beams incident on the respective diffraction areas of the optical path branching means are diffracted into different directions by the diffraction areas of the optical path branching means, then transmitted through the optical member, and directed toward the photodetector.
Since at least one light receiving section of the photodetector is divided into the portion for receiving the return light beam diffracted by one diffraction area of the optical path branching means and the portion for receiving the return light beam diffracted by the other diffraction area, the return light beams diffracted into different directions by the respective diffraction areas of the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector.
The return light beams received by the respective portions of the light-receiving section of the photodetector are photoelectrically converted by the photodetector and supplied as detection signals to the signal processing circuit. In the signal processing circuit, predetermined arithmetic processing is carried out on the basis of the detection signal, thereby generating a reproduction signal and generating a focusing error signal by a so-called Foucault method.
Meanwhile, in the case where signals are to be recorded to and/or reproduced from the optical disc in this optical disc device, first the optical pickup is moved in the direction of radius by the access mechanism so as to access a desired recording track, as described above. In this case, the position of the light beam converging means of the optical pickup with respect to the optical member may be deviated into the direction of radius of the optical disc from the normal position because of inertia. When the position of the light beam converging means with respect to the optical member is deviated in the direction of radius of the optical disc from the normal position, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In the optical disc device according to the present invention, the optical path branching means of the optical pickup has at least two diffraction areas for diffracting the return light beam into different directions, and the boundary between these diffraction areas is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the optical path branching means. The individual parts of the return light beam generated by asymmetrical splitting by the optical path branching means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the optical member can be detected by carrying out predetermined arithmetic processing in the signal processing circuit on the basis of the detection signal from the light-receiving section of the photodetector.
According to the optical disc device of the present invention, since the position deviation of the light beam converging means with respect to the optical member at the time when causing the optical pickup to access a desired recording track on the optical disc can be detected in the above-described manner, the position of the light beam converging means can be instantaneously recovered to secure the accuracy and stability of the access operation and to realize the high-speed access property.
Also, in this optical disc device according to the present invention, the optical path branching means of the optical pickup for separating the optical path of the return light beam directed toward the photodetector from the optical path of the light beam emitted from the light source and for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the optical member, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical disc device can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
Another optical disc device according to the present invention includes: disc rotating means for rotating an optical disc; an optical pickup for carrying out recording and/or reproduction of signals by irradiating with a light beam a signal recording surface of the optical disc rotated by the disc rotating means; a signal processing circuit for processing a detection signal from the optical pickup; and an access mechanism for moving the optical pickup in the direction of radius of the optical disc.
In this optical disc device, the optical pickup includes a light source for emitting the light beam, light beam converging means for converging the light beam emitted from the light source and for irradiating the signal recording surface of the optical disc with the converged light beam, a photodetector having a light-receiving section for receiving a return light beam reflected by the signal recording surface of the optical disc, an optical member arranged between the light source and photodetector on one side and the light beam converging means on the other side, for transmitting the light beam emitted from the light source and for transmitting the return light beam directed toward the photodetector, optical path branching means integrally formed with the optical member for separating the optical path of the light beam emitted from the light source and the optical path of the return light beam reflected by the signal recording surface of the optical disc, return light beam splitting means integrally formed with the optical member for splitting the return light beam passed through the optical path branching means into at least two beams, and a biaxial actuator for moving the light beam converging means into biaxial directions, that is, the direction of radius of the optical disc and the direction toward and away from the optical disc. The return light beam splitting means has at least two surfaces having different normal vectors, and the boundary between these surfaces is inclined at a predetermined angle with respect to a direction corresponding to the direction of radius of the optical disc. At least one light-receiving section of the photodetector is divided into a portion for receiving one return light beam generated by the return light beam splitting means and a portion for receiving the other return light beam.
In this another optical disc device according to the present invention, the optical disc as a recording medium is rotated by the disc rotating means. Then, when signals are to be recorded to and/or reproduced from the optical disc rotated by the disc rotating means, a light beam is first emitted from the light source of the optical pickup to the optical disc rotated by the disc rotating means. The optical pickup is moved in the direction of radius of the optical disc by the access mechanism so as to access a desired recording track.
The light beam emitted from the light source is transmitted through the optical member and directed toward the light beam converging means. The light beam is then converged by light beam converging means and then cast onto the signal recording surface of the optical disc.
In the case where the spot of the light beam cast on the signal recording surface of the optical disc is deviated from a predetermined recording track on the signal recording surface of the optical disc, or in the case where no focal point is formed on the signal recording surface of the optical disc, the biaxial actuator is driven on the basis of a tracking error signal or a focusing error signal from the signal processing circuit, and the light beam converging means is moved by the biaxial actuator into the direction of radius of the optical disc or into the direction toward and away from the optical disc. Thus, the spot of the light beam converged by the light beam converging means and cast onto the signal recording surface of the optical disc constantly follows a predetermined recording track on the signal recording surface of the optical disc and forms a focal point on the signal recording surface of the optical disc.
The light beam cast on the signal recording surface of the optical disc is reflected by the signal recording surface of the optical disc and thus becomes a return light beam including a signal component. The return light beam passes again through the light beam converging means and then becomes incident on the optical member.
The return light beam incident on the optical member has its optical path separated from the optical path of the light beam emitted from the light source, by the optical path branching means formed integrally with the optical member. Specifically, the optical path branching means includes, for example, a hologram formed on the surface of the optical member. As the return light beam is diffracted by the hologram into the direction toward the photodetector, the optical path of the return light beam is separated from the optical path of the light beam emitted from the light source.
The return light beam having its optical path branched by the optical path branching means is then split into at least two beams by the return light beam splitting means integrally formed with the optical member.
Since the return light beam splitting means has at least two surfaces having different normal vectors, the return light beam incident on the return light beam splitting means is split along the boundary between the surfaces. The beams generated by splitting proceed in different directions in accordance with the normal vectors of the surfaces on which they are incident, and are directed toward the photodetector.
Since at least one light receiving section of the photodetector is divided into the portion for receiving one return light beam generated by the return light beam splitting means and the portion for receiving the other return light beam, the return light beams generated by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector.
The return light beams received by the respective portions of the light-receiving section of the photodetector are photoelectrically converted by the photodetector and supplied as detection signals to the signal processing circuit. In the signal processing circuit, predetermined arithmetic processing is carried out on the basis of the detection signal, thereby generating a reproduction signal and generating a focusing error signal by a so-called Foucault method.
Meanwhile, in the case where signals are to be recorded to and/or reproduced from the optical disc in this optical disc device, first the optical pickup is moved in the direction of radius by the access mechanism so as to access a desired recording track, as described above. In this case, the position of the light beam converging means of the optical pickup with respect to the optical member may be deviated into the direction of radius of the optical disc from the normal position because of inertia. When the position of the light beam converging means with respect to the optical member is deviated in the direction of radius of the optical disc from the normal position, the spot of the return light beam incident on the optical member is deviated in the direction corresponding to the direction of radius of the optical disc, on the optical path branching means.
In this another optical disc device according to the present invention, the return light beam splitting means of the optical pickup has at least two surfaces of different normal vectors and the boundary between these surfaces is inclined at a predetermined angle with respect to the direction corresponding to the direction of radius of the optical disc. Therefore, in the case where the position of the light beam converging means is deviated in the direction of radius of the optical disc from the normal position, the return light beam is split asymmetrically by the return light beam splitting means. The individual parts of the return light beam generated by asymmetrical splitting by the return light beam splitting means are received by the corresponding portions of the light-receiving section of the photodetector. Therefore, the position deviation of the light beam converging means with respect to the optical member can be detected by carrying out predetermined arithmetic processing in the signal processing circuit on the basis of the detection signal from the light-receiving section of the photodetector.
According to this another optical disc device of the present invention, since the position deviation of the light beam converging means with respect to the optical member at the time when causing the optical pickup to access a desired recording track on the optical disc can be detected in the above-described manner, the position of the light beam converging means can be instantaneously recovered to secure the accuracy and stability of the access operation and to realize the high-speed access property.
Also, in this another optical disc device according to the present invention, the return light beam splitting means of the optical pickup for generating a focusing error signal by the Foucault method is used for detecting the position deviation of the light beam converging means with respect to the optical member, instead of additionally providing any means for detecting the position deviation of the light beam converging means. Therefore, the optical disc device can realize the high-speed access property by appropriately and simply detecting the position deviation of the light beam converging means, without causing the increase in the number of components, the increase in the size of the device itself and the rise in cost.
FIG. 1 is a perspective view schematically showing a conventional optical pickup.
FIG. 2 is a view for explaining the deviation of an objective lens in the direction of radius of an optical disc at the time of access by the optical pickup.
FIG. 3 is a block diagram showing an exemplary structure of an optical disc device to which the present invention is applied.
FIG. 4 is a perspective view schematically showing an optical pickup to which the present invention is applied.
FIG. 5 is a side view schematically showing the state inside the optical pickup for explaining the positional relation of an integrated optical element to which the present invention is applied in the optical pickup.
FIG. 6 is a side view schematically showing the state inside the integrated optical element to which the present invention is applied.
FIG. 7 is a perspective view schematically showing the positional relation of individual members constituting the optical pickup to which the present invention is applied.
FIGS. 8A to 8C show the relation between the position of an objective lens in the optical pickup to which the present invention is applied and the position of a return light spot formed on a hologram. FIG. 8A shows the state where the objective lens is located at a normal position. FIGS. 8B and 8C show the state where the position of the objective lens is deviated.
FIG. 9 is a side view schematically showing the state inside another integrated optical element to which the present invention is applied.
FIG. 10 is a perspective view schematically showing the positional relation of individual members constituting another optical pickup to which the present invention is applied.
FIG. 11 is an enlarged perspective view showing essential portions of an optical member provided in another optical pickup to which the present invention is applied.
FIGS. 12A to 12C show the relation between the position of an objective lens in another optical pickup to which the present invention is applied and the position of a return light spot formed on a Foucault prism. FIG. 12A shows the state where the objective lens is located at a normal position. FIGS. 12B and 12C show the state where the position of the objective lens is deviated.
FIG. 13 is a side view schematically showing the state inside still another integrated optical element to which the present invention is applied.
FIG. 14 is a perspective view schematically showing the positional relation of individual members constituting still another optical pickup to which the present invention is applied.